In sucrose molecule the glycosidic linkage is formed by the OH group on the anomeric carbon of α-D-glucose and the OH group on the anomeric carbon of β-D-fructose.
As seen, in either alpha d-glucose or beta d-fructo furanose may react to give sucrose.
Let us examin.
Alpha D-gluco Pyranose gives an intermediate 1 and 2 by protonation at anomeric carbon.
Similarly Beta D-fructo furanose gives an intermediate 3 and 4 by protonation at anomeric carbon.
If you examine , structure 3 is more stable then structure 4.
The negative inductive effect of CH2OH in fructofuranose destablizes this intermediate 4.
Hence structure 2 , an intermediate of aplha D-gluco pyranose (more stable) attacks beta D-fructo furanose togive sucrose.
The above diagrams are author drawn in CHEM DRAW